Universal parallel adapter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Universal Parallel Adapter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Computers

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The universal parallel adapter is designed to connect various devices with digital inputs to a computer. For example, it can be used to write information to ROM, directly control stepper motors, to establish various electronic circuits as an emulator, etc. a very real risk of port failure, since its outputs are not protected and are designed to connect only one output, and repair may require replacing the motherboard. In addition, to connect anything to the parallel port, you must first turn off the computer. The adapter eliminates these problems and allows you to think first of all about the circuit being developed, and not about how not to burn the computer in the process of creating it.

Universal Parallel Adapter

The idea of using a parallel port for issuing and receiving digital signals with TTL levels is not new, for example, a similar scheme is given in [1]. The adapter proposed here is characterized by simplicity, with sufficient capabilities for a large number of applications. In addition, if after some time you need to increase the number of inputs / outputs, you can simply assemble the same circuit and connect it according to the table below. Although if it is assumed that the conclusions of one circuit will not be enough right away, it is better to use a more powerful option. The circuit consists of three registers and one multiplexer. All registers are enabled in the same way, with the exception of the third, its outputs can be switched to a high-resistance state, therefore, a control signal to enable the OE outputs is also connected to it. The information inputs of all registers are combined and connected to the corresponding outputs of the computer's parallel port, since the TTLSH series is used, it is permissible to load one port output on several microcircuit inputs. For gating, the control lines of the port are used, connected to the inputs of the C registers. To increase the number of inputs, a D4 multiplexer is used.

The circuit is connected to a parallel port, it is also necessary to supply + 5V power to the microcircuits, it is best to use a computer power supply for this. In my version, the assembled circuit is located inside the computer, it is connected to the internal LPT port connector on the system board, it uses a 4-pin connector for power supply, and the working outputs are routed to a 32-pin connector mounted in a plug from the 5,25 compartment on the front panel. The supply voltages +5, +12 volts are output to the same connector. If it is necessary to increase the number of outputs, you can assemble a second such block and connect it in accordance with the table below to the first one connected to the computer. In this case, several additional entrances and exits will appear, but the access time will increase. O1...O24 circuits are used to connect to an external device, of which O1...O16 are ordinary outputs, and O17-O24 can be used as inputs or outputs. The O16 circuit is used in parallel for internal needs.

Parallel port connection
Port pin A type Output name Adapter chain
2 O D0 IN1
3 O D1 IN2
4 O D2 IN3
5 O D3 IN4
6 O D4 IN5
7 O D5 IN6
8 O D6 IN7
9 O D7 IN8
1 O -STROBE IN9
14 O -AUTO FD IN10
16 O -INIT IN11
17 O -SLCT IN IN12
10 I -ACK IN13
11 I BUSY IN14
12 I PE IN15
13 I SLCT IN16
18 25 ... - GND total

Connecting a second adapter to increase the number of pins
First Second First Second
O1 I1 O9 I9
O2 I2 O10 I10
O3 I3 O11 I11
O4 I4 O12 I12
O5 I5 O17 I13
O6 I6 O18 I14
O7 I7 O19 I15
O8 I8 O20 I16

The program must be written for each specific case of using the device separately, so I do not give any options here, but only consider the basic principles of programmatic control of the circuit. Almost any programming language has functions that allow you to write a number at a given address to an I / O port. The schema is controlled through calls to such functions. To write an 8-bit number to the buffer register of the circuit, it is necessary to write it to the data register of the parallel port, then write to the control register any number that has a unit in the corresponding bit (corresponding to pin C of the selected buffer register) and then zero to it. To read 4 bits of data, simply read the port status register, to read the remaining bits, first change the state of the O16 line. It must be taken into account that some input and output lines of the port are inverted. The register addresses for LPT1 are shown in the table and are correct for most computers, but BIOS data should be used to correctly determine the addresses.
Data register 378 h
Status register 379 h
Control register 37Ah

Publication: cxem.net

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